The present invention relates to a temperature-based cooling fan control system, and more particularly to a cooling fan control system that includes a thermistor, a voltage amplification system, a rotating speed control system, and means for setting rotating speed to compare a voltage needed by a basic rotating speed with an amplified voltage and thereby adjust fan rotating speed. The control structure also includes a timing trigger capacitor to periodically actuate the cooling fan when the fan is temporarily stopped under an external force.
FIG. 1 illustrates a circuit diagram of a conventional cooling fan. As shown, the circuit includes a magnetic induction device 1xe2x80x2 that receives bias voltage supplied by a voltage source Vcc via a bias resistor R1xe2x80x2. A permanent magnet is included in the magnetic induction device 1xe2x80x2. By means of polar changes over single magnetic pole (N and S pole), current is caused to pass coils L1xe2x80x2 and L2xe2x80x2. A forward diode D1xe2x80x2 is connected to the voltage source Vcc to avoid internal elements of the cooling fan from burning out. With these arrangements, the fan rotates at a fixed speed and is not changed by any factor. Current keeps flowing through coils L1xe2x80x2 and L2xe2x80x2 even when the cooling fan is temporarily stopped. Furthermore, two zener diodes D3xe2x80x2 and D4xe2x80x2 are connected to outputs of coils L1xe2x80x2 and L2xe2x80x2, respectively, to stabilize and control voltage, so that the fan rotates at a fixed voltage value to avoid or reduce electromagnetic noise.
Following disadvantages are found in the above-described conventional cooling fan:
(1) The fan rotating speed can not be adjusted in response to changes in ambient temperature.
(2) Current keeps flowing through coils when the fan is temporarily stopped and internal elements thereof tend to burn out.
(3) Polar changes over single pole cause the fan to always rotate at a fixed speed.
It is therefore a primary object of the present invention to provide a structure that uses temperature to control a cooling fan. A thermistor is included in the control structure to measure ambient temperature for use as a basis to adjust a terminal voltage, and a voltage amplification system amplifies the terminal voltage and transmits the amplified voltage to a rotating speed control system. The present invention also includes a magnetic induction system to provide multiple magnetic pole pairs, so that repulsion between similar magnetic poles transmits a signal to the rotating speed control system. The rotating speed control system compares a voltage needed by a basic rotating speed as set by a rotating speed setting means with the amplified voltage, in order to change the fan rotating speed.
Another object of the present invention is to provide the above cooling fan control structure in which a timing trigger capacitor is connected to the rotating speed control system, so that the fan in a temporarily stopped state under an external force can be periodically actuated by the timing trigger capacitor to rotate and diffuse heat.
It is known a thermistor generates a negative resistance against ambient temperature. The thermistor included in the cooling fan control structure of the present invention measures temperature a t the end of the thermistor and a terminal voltage thereof is adjusted according to the measured temperature. The adjusted terminal voltage is amplified by the voltage amplification system according to a set voltage amplifying degree and the amplified voltage is transmitted to the rotating speed control system. Meanwhile, an induction signal indicating repulsion between two similar magnetic poles in the magnetic induction system is also transmitted to the rotating speed control system. The rotating speed control system compares a voltage needed by a basic rotating speed as set by the rotating speed setting means with the amplified voltage, so that current flowing through coils can be adjusted according to the measured temperature to cause the cooling fan to rotate at variable speed. In the event the fan is temporarily stopped under an external force, the timing trigger capacitor may periodically actuate the fan to rotate at set intervals.